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Introducing asymmetry in your bevels is a way of thinning your blade near the cutting edge without lowering your bevel angles excessively and causing weakness in your edge or in extreme cases, failure to even form an edge (it would just crumble, leaving large chips in the edge). The trade-off is a "steering" effect that is caused by unequal forces acting on either side of the edge. The side with the larger bevel would encounter a larger force resisting the cut and so the blade would tend to veer away from that side. To counteract this effect, the angle at which the large bevel is ground can be lowered relative the the small bevel to more evenly distribute the forces.

If you feel you want to keep your edge thin but add even more strength, you can add a microbevel to anything and it can be a single extra bevel at a higher angle or it can be two extra bevels depending on how you like your edges to perform. When I apply a microbevel, I will generally add a tiny bevel at a large angle (25-60 deg) on the right side only for a right handed knife.

I don't do this for AS, in particular but mainly for knives that are exceedingly thin at the edge (single bevel or ultra thinned knives), blades that are hardened to the point they lose their toughness (for AS I might put a micro on anything over 61 hrc depending on the user), blades made of very high carbon steel (significantly more than 1%) since the high carbide volume will lower the stability of the edge or blades where the carbide size is fairly large and will simply not form a decent edge at 10-15 deg on a bevel (conventional German knives, for example).

Ok good to know, i have actually noticed that with a coworkers knife, some german made knife, i sharpened it and it was super sharp, i then applied a microbevel and it was significantly duller than before had to redo the entire process but it wouldn't handle a microbevel for some reason I'm guessing the steel.

but i always add a microbevel to my misonos about 45 deg or so, and i haven't noticed an ill effects to far, i also add one to my Kono HD since i use it so much.

By AS, you mean asymmetric? For future reference, AS always means Aogami Super/Blue Super. Asymmetric edges are good for single beveled knives of any kind. Jon puts a micro on Suisin Inox blades (19C27 is pretty high carbon and it is pretty hard on that line). HOWEVER, it really just depends on how much you've thinned it compared to what it can take. That, in turn depends on what the user does with it. This is one of those questions that is subjective and user-specific. For example, I hardly EVER use microbevels on my own knives. I'm pretty gentle with them and it's nice when I actually get to sharpen them. I have a friend, though who is a pro and is pretty careless with his knives. I use microbevels on EVERYTHING for that dude.

For those of you on the forum who think I might be talking about you on that last part, I'm not.

I would say knives with asymmetric blades! Most Japanese knives I've seen had a convex front (right, with kanji inscription) blade and a flat back. The front side has a very large convex bevel while the back almost none. Typical would be the front being sharpened at eventually 10 degrees, and the back hardly sharpened but just stropped at 15.

I am a bit confused. How does shifting the edge over a bit allow you to thin it and maintain more edge strength/stability? I kind of understand why the Japanese may single bevel knives with a hollow grand backside, but I am having trouble figuring out the 70/30 type grinds.

I can't draw it for you right now but if you draw bevels at the same angle as shown in the first edge and the second to last edge (going from left to right) here: http://zknives.com/knives/articles/knifeedgetypes.shtml, you will see that the thickness of the knife within the bevel is thinner behind the edge for the asymmetric version.

In those pics, it actually looks thicker to me. I can see how leaving more of the "short" side of the blade flat would mght you a similar effect to a chisel grind, but I'm still not seeing how actually it gets the part right above the edge thinner.

Originally Posted by tk59

I can't draw it for you right now but if you draw bevels at the same angle as shown in the first edge and the second to last edge (going from left to right) here: http://zknives.com/knives/articles/knifeedgetypes.shtml, you will see that the thickness of the knife within the bevel is thinner behind the edge for the asymmetric version.